A catalyst for purifying components in an exhaust gas discharged from a combustion chamber of an internal combustion engine is described in the patent literature 1.
This catalyst has an element for activating an oxidation reaction or a reduction reaction of the component in the exhaust gas (hereinafter, this element may be referred to as—active element—) and a carrier for carrying the active element, which carrier being comprised of a composite oxide.
Further, this catalyst has a property in which the active element transforms into the carrier as a solid solution when an atmosphere in the catalyst is an oxidation atmosphere and the active element precipitates from the carrier when the atmosphere in the catalyst is a reduction atmosphere.